We use a convection oven successfully for COD, and the digestion temperature specified for our TKN is 100 C, so we use a beaker of boiling water and insure that the water is at a rolling boil before inserting the tubes for digestion. We run a QA sample which each analysis and have found our results are repeatable and within the expected precious and accuracy for our kits. The specified COD QA is potassium hydrogen phthalate, readily available at a reasonable price.

Thank you